Almost all vehicles presently produced include some type of a passive restraint system to protect vehicle occupants, or others, during a vehicle impact event. Such passive restraint systems may include, for example, front and side airbags within the passenger compartment, seat belt pretensioners, and pedestrian airbags near the front of a vehicle. In order for the passive restraints to operate quickly when needed, and only when actually needed, sensor systems must be mounted on the vehicle to determine the severity and type of impact and actuate the proper passive restraint devices.
Some types of sensors used for impact measurements on vehicles approximate or infer the type of impact being experienced. Such sensors may be, for example, accelerometers, pressure sensors and crush-zone switches. While they can work adequately, it is desirable to improve the discrimination ability of vehicle impact sensing systems thus improving the passive restraint deployment decision upon vehicle impact.
Accelerometers, when used alone, may require very complex computer algorithms in order to properly distinguish various impact events. Pressure sensors have also been suggested, but may be too susceptible to changes to the surrounding vehicle environment. Further, simple switch contacts around the vehicle perimeter may be used but give little information regarding the intruding object's profile and/or velocity, making passive restraints deployment decisions difficult. Consequently, a desire exists to provide for more accurate sensing that will allow for discrimination between different types and severities of vehicle impact events to provide improved passive restraint actuation decisions, within minimal time frames. Further, a diagnostics system is desirable that will monitor the sensors to assure proper operation.